In cancer research, defense applications, and other areas, directed energy is utilized to induce a biological response in a material both in-vivo and in-vitro. Biological responses include induced cell apoptosis, DNA transfection, exciting and inhibiting neuron action potentials, etc. Imaging of the spatial and temporal response to directed energy provides information to improve the delivery of directed energy impulses, through an enhanced understanding of the driving mechanisms responsible for a desired biological response. This will increase the effectiveness of directed energy cancer treatment, and the effectiveness of non-lethal weapons system.
Currently, all optical methods for high spatial resolution, fast (<100 ns) imaging of mechanical phenomena in high strength electric fields are limited to pump probe photography (PPP) and Schlieren imaging. PPP and Schlieren photography are based on the deflection of a laser beam as it travels through a medium of interest. However, these methodologies require short pulsed lasers with pulse durations less than 20 ns and cameras with high contrast and time resolution to achieve the necessary time resolution and contrast required to image multi-physics phenomena, such as mechanically induced refractive index gradients.
In the past, the Kerr effect has been utilized to map electric field distributions in liquids. The Kerr effect is the polarization shift of an optical beam, due to the alignment of water molecules acting as a crystal when exposed to an external electric field. For example, the electric field distribution has been mapped in non-conductive media during the study of pre-breakdown phenomena.
However, the combination of deflection based imaging and Kerr effect imaging to characterize directed energy dosimetry achieving micron spatial resolution and sub-nanosecond time resolution has not been demonstrated.
The probe beam deflection technique (PBDT) correlates the deflection of a laser beam propagating through a medium of interest with any detectable thermal or acoustic disturbance in the media. PBDT and PPP both require a repetitive/stable event to image a time-lapse sequence, however unlike PPP, PBDT does not require a short pulse laser to illuminate a camera aperture to acquire an image. PBDT has been utilized previously for ultrasound and photoacoustic measurement, as well as imaging. The technique has been applied to the measurement of acoustic waves in gas phase, namely the gas coupled laser acoustic detector (GCLAD), where detection bandwidth is limited by the speed of sound in air. PBDT has also been shown to be a passive wide band ultrasonic sensor in liquids. Imaging of an ultrasonic target, such as soft tissue, has been demonstrated in photo-acoustics, and imaging of a photoacoustic wave has been shown. In addition, PBDT has been used to measure acoustic waves generated by a nanosecond electric pulse (nsEP) in one-dimension.
Currently, no systems or techniques are available for measuring both mechanical and electromagnetic responses of a medium to a directed energy pulse.